1. Field of the Invention
The principles of the present invention generally relate to a system and method for measuring a rate of biological tissue healing. More specifically, the principles of the present invention relate to measuring rate of biological tissue healing by normalizing color of an image of a tissue site and identifying colors of tissue site (e.g., wound) areas that are associated with a phase of healing.
2. Description of the Related Art
The field of wound therapy has advanced in recent years. One of the advancements of wound healing therapy has been the development of vacuum assisted wound healing. The application of reduced or negative pressure to a wound has been clinically shown to improve blood flow at the wound or tissue site, increase tissue growth, reduce infection, and improve healing time. Caregivers and clinicians may use such vacuum assisted wound healing to treat a variety of chronic and acute wound types, such as pressure ulcers, diabetic wounds, abdominal wounds, partial-thickness burns, trauma wounds, flaps and grafts.
Background on Wounds and Wound Healing Processes
A wound is generally defined as a break in the epithelial integrity of the skin. Such an injury, however, may be much deeper, including the dermis, subcutaneous fat, fascia, muscle, and even bone. Proper wound healing is a highly complex, dynamic, and coordinated series of steps leading to tissue repair. Acute wound healing is a dynamic process involving both resident and migratory cell populations acting in a coordinated manner within the extra-cellular matrix environment to repair the injured tissues. Some wounds fail to heal in this manner (for a variety of reasons) and may be referred to as chronic wounds.
Following tissue injury, the coordinated healing of a wound will typically involve four overlapping but well-defined phases: hemostasis, inflammation, proliferation, and remodeling. Hemostasis involves the first steps in wound response and repair that are bleeding, coagulation, and platelet and complement activation. Inflammation peaks near the end of the first day. Cell proliferation occurs over the next 7-30 days and involves the time period over which wound area measurements may be of most benefit. During this time fibroplasia, angiogenesis, re-epithelialization, and extra-cellular matrix synthesis occur. The initial collagen formation in a wound typically peaks in approximately 7 days. The wound re-epithelialization occurs in about 48 hours under optimal conditions, at which time the wound may be completely sealed. A healing wound may have 15% to 20% of full tensile strength at 3 weeks and 60% of full strength at 4 months. After the first month, a degradation and remodeling stage begins, wherein cellularity and vascularity decrease and tensile strength increases. Formation of a mature scar often requires 6 to 12 months.
Efforts in the Related Art to Measure Wound Healing Processes
Because wound treatment can be costly in both materials and professional care time, a treatment that is based on an accurate assessment of the wound and the wound healing process can be essential. There are a few wound parameters that may assist a clinician in determining healing progress of a wound. For example, wound area and volume measurements may provide a clinician with knowledge as to whether or not a wound is healing and, if the wound is healing, how rapidly the wound is healing. Wound assessment is an important to properly treating a wound as improper or incomplete assessment may result in a wide variety of complications. Infections at a tissue site that go untreated may result in permanent damage or even death to a patient.
While wound measurement is a parameter that is beneficial to a clinician to determine wound healing progress, the size of the wound may not provide a clinician with enough information to fully assess whether or how a wound is healing. For example, while a wound may reduce in size, certain parts of a wound may become infected. A clinician often examines wound tissue for its color and texture to determine how a wound is healing. Wound tissue includes a wound bed and periwound areas or wound edges. Health of a wound may be determined by color of tissue. Conversely, certain problems may be detected from the color of wound tissue. For example, normal granulation tissue has a beefy, red, shiny textured appearance and bleeds readily, whereas necrotic tissue (i.e., dead tissue) may either be yellow-gray and soft, generally known as “slough” tissue, or hard and black/brown in color, generally known as “eschar” tissue. A clinician may observe and monitor these and other wound tissues to determine wound healing progress of the overall wound and specific wound regions.
While consistent wound measurement is a factor for accurately determining changes in wound size, so too is measurement of different wound tissue. Although texture of wound tissue is indicative of wound healing, color can also be used. One problem with color of wound tissue is that colors can often be altered depending on lighting. For example, a wound under incandescent lighting may have a different color appearance from a wound under fluorescent lighting. Also, different clinicians may have different color perception. For example, one clinician may have strong color perception while another may be color blind in one or more colors, thereby providing both with different interpretation of color of wound tissue.
While a number of techniques have been developed to estimate the size of a wound, there are but a few techniques for measuring different types of wound tissue despite the inherent value provided to a clinician in knowing size and color of different wound tissue. One technique includes placing a clear film over a wound and using a soft-tipped pen to color different wound tissues on the film, thereby making a record of the wound tissues. This process may be repeated to record wound healing over time. This process also suffers due to lighting conditions, color sensitivity of clinicians, capability of a clinician to accurately draw on the clear film, and inherent problems from contacting the film onto the wound tissue. Another technique includes making an outline of the wound on the film, scanning the image into a computer, and then drawing an estimation of the different wound tissue on the computer.